For many years, turbochargers have been widely used in internal combustion engines. By harnessing the flow of hot exhaust gas exiting an engine's combustion chamber, turbochargers are able to improve the engine's volumetric efficiency. Turbochargers, as well as other types of turbomachinery, generally require vibration damping and thrust load provisions to accommodate their components that rotate at high angular velocity.
Typically, a bearing system is provided in a turbocharger for vibration damping and accommodating thrust loads. For example, bearing systems are typically located adjacent the rotor shaft of turbomachinery to dampen vibrations of the shaft. Where rotor shaft speeds and external influences on shaft motion are high, the ability to effectively dampen the rotor shaft has a close relationship to the performance of the engine as a whole. In addition to dampen vibrations of the rotor shaft, an effective bearing system must be able to handle axial thrust loads imposed on the rotating assembly of the turbocharger by the compressor and turbine wheels. Furthermore, the bearing system must also be able to operate in view of thermal loading of the assembly due to the very hot exhaust gases exiting the engine combustion chamber via the turbine wheel. Without damping and thrust provisions, a rotor shaft would transmit forces through the turbomachinery that would limit the performance of the engine, as well as cause noise, fretting, loosening of joints, and reduced service life of the turbomachinery as a whole and its individual parts.
Modern engines typically run at high pressure ratios that create shaft vibrations and thrust loads that common, inexpensive bearings (e.g., convention journal and thrust bearings) within existing turbochargers typically are not able to dampen. Also, most bearings are not very effective within existing turbochargers because they are not able to resist the high heat. Premium bearings, such as hybrid ceramic ball bearings, are able to withstand the vibrations and loads created by modern engines. The premium bearings are also able to tolerate exposure to high heat. However, the cost of utilizing premium bearings is prohibitive for most applications.
Accordingly, there exists a need for a turbocharger with a bearing system having a high thrust capacity that is cost effective.